Castro culture (Galician: cultura castrexa, Portuguese: cultura castreja, Asturian: cultura castriega, Spanish: cultura castreña, meaning "culture of the hillforts") is the archaeological term for the material culture of the northwestern regions of the Iberian Peninsula (present-day northern and central Portugal together with the Spanish regions of Galicia, Asturias, and western León) from the end of the Bronze Age (c. 9th century BC) until it was subsumed by Roman culture (c. 1st century BC). It is the culture associated with the Celtic Gallaecians and Astures.

The most notable characteristics of this culture are its walled oppida and hillforts, known locally as castros, from Latin castrum 'castle', and the scarcity of visible burial practices, in spite of the frequent depositions of prestige items and goods, swords and other metallic riches in rocky outcrops, rivers and other aquatic contexts since the Atlantic Bronze Age. This cultural area extended east to the Cares river and south into the lower Douro river valley.

The area of Ave Valley in Portugal was the core region of this culture, with many small Castro settlements, but also including larger oppida, the cividades (from Latin civitas 'city'), some known as citânias by archaeologists, due to their city-like structure: Cividade de Bagunte (Civitas Bogonti), Cividade de Terroso (Civitas Terroso), Citânia de Briteiros, and Citânia de Sanfins.

The Castro culture emerged during the first two centuries of the first millennium BC, in the region extending from the Douro river up to the Minho, but soon expanding north along the coast, and east following the river valleys, reaching the mountain ranges which separate the Atlantic coast of the Iberian peninsula from the central plateau or meseta. It was the result of the autonomous evolution of Atlantic Bronze Age communities, after the local collapse of the long range Atlantic network of interchange of prestige items.

From the Mondego river up to the Minho river, along the coastal areas of northern Portugal, during the last two centuries of the second millennium BC a series of settlements were established in high, well communicated places, radiating from a core area north of the Mondego, and usually specializing themselves in the production of Atlantic Bronze Age metallurgy: cauldrons, knives, bronze vases, roasting spits, flesh-hooks, swords, axes and jewelry relating to a noble elite who celebrated ritual banquets and who participated in an extensive network of interchange of prestige items, from the Mediterranean and up to the British Isles. These villages were closely related to the open settlements which characterized the first Bronze Age, frequently established near the valleys and the richer agricultural lands.

From the beginning of the first millennium, the network appears to collapse, possibly because the Iron Age had outdated the Atlantic tin and bronze products in the Mediterranean region, and the large-scale production of metallic items was reduced to the elaboration of axes and tools, which are still found buried in very large quantities all along the European Atlantic coast.

During the transition of the Bronze to the Iron Age, from the Douro in modern northern Portugal and up along the coasts of Galicia until the central regions of Asturias, the settlement in artificially fortified places substituted the old open settlement model. These early hill-forts were small (1 ha at most), being situated in hills, peninsulas or another naturally defended places, usually endowed with long range visibility. The artificial defences were initially composed of earthen walls, battlements and ditches, which enclosed an inner habitable space. This space was mostly left void, non urbanised, and used for communal activities, comprising a few circular, oblong, or rounded squared huts, of 5 to 15 meters (16–49 ft) in the largest dimension, built with wood, vegetable materials and mud, sometimes reinforced with stony low walls. The major inner feature of these multi-functional undivided cabins were the hearth, circular or quadrangular, and which conditioned the uses of the other spaces of the room.

In essence, the main characteristic of this formative period is the assumption by the community of a larger authority at the expense of the elites, reflected in the minor importance of prestige items production, while the collective invested important resources and labour in the communal spaces and defences.